How does Shatter work?

I have searched all of the forums and the wiki as much as I can, and have still not found very much on Shatter. I understand that if an enemy is frozen when you deal the killing blow, they are shattered, but I've noticed that sometimes when I freeze something, and it still has a ton of life left, I can still shatter it with my next blow. It seems fairly random so far, but I just wondered if there is a formula for it, or if it is just coincidence that I crit or something that damages them so much at one time while they are frozen.

Does anyone know of any additional info on shatter?

Can't find a source for this right now, but I think enemies shatter when you reduce their health to below 10% of max hp while they are frozen.